Abstract:
The bulk flow motion in the Local Universe is a collective phenomenon arising from the peculiar motions of matter structures, which, instead of moving randomly, appear to exhibit an approximately dipolar velocity flow. For its study, we conducted a directional analysis investigating, through the Hubble-Lemaître diagram, the angular dependence of the Hubble constant H_0 on the celestial sphere using a sample of Type Ia Supernovae from the Pantheon+ catalog in the Local Universe (0.015 ≤ z ≤ 0.06), considering an angular resolution to scan uniformly the celestial sphere with N=192 spherical caps. Our analysis reveals a statistically significant dipolar variation of H_0 with over 99.9% confidence level, showing that matter structures follow a dipolar bulk flow towards (l,b) = (326.1° ± 11.2°, 27.8° ± 11.2°), near the Shapley supercluster (l_{Shapley}, b_{Shapley}) = (311.5°, 32.3°), with a velocity of 132.14 ± 109.3 km/s at an effective distance of 102.83 ± 10.2 Mpc. The antipodal direction of this dipole points near the cosmic void known as the Dipole Repeller. Our analyses confirm that the approximately dipolar gravitational system Shapley-Dipole Repeller effectively explains the observed velocity field of the bulk flow in the Local Universe. Additionally, we conducted robustness tests that support our findings. We also obtained a measurement of the Hubble constant H_0 = 70.39 ± 1.4 km/s/Mpc, which was derived using the first-order approximation of the Hubble-Lemaître law, that is, a cosmological model-independent methodology.
